Seed rain of fleshy and dry propagules in different habitats in the temperate rainforests of Chiloé Island, Chile

Abstract

In temperate rainforests on Chiloé Island in southern Chile (42°S), most canopy trees bear fleshy, avian‐dispersed propagules, whereas emergent tree species have dry, wind‐borne propagules. In the present study, the following hypothesis was tested: regardless of species, fleshy propagules are deposited in greater numbers in canopy gaps and in forest margins and hence have a more heterogeneous seed shadow than wind‐dispersed propagules. To test this hypothesis, the seed rains of these two types of propagules were compared in the following forest habitats: (i) tree‐fall gaps (edges and centre); (ii) forest margins with adjacent pastures; and (iii) under closed canopy (forest interior). Seed collectors (30‐cm diameter) were placed in two (15 and 100 ha) remnant forest patches (n = 60–100 seed collectors per patch) distributed in the four habitats. Seeds were retrieved monthly from each collector during two reproductive seasons (1996, 1997). In both years, the seed rain was numerically dominated by two species with dry propagules (Laureliopsis philippiana and Nothofagus nitida) and three species with fleshy fruits (Drimys winteri, Amomyrtus luma, and Amomyrtus meli). The seed shadows of the two species with dry, wind‐dispersed seeds differed markedly. Seeds of L. philippiana were deposited predominantly in canopy openings, whereas N. nitida seeds fell almost entirely in the forest interior. The fleshy‐fruited species, Drimys and Amomyrtus spp., had similar seed deposition patterns in the various habitats studied, but the between‐year differences in seed rain were greater in Drimys winteri than in Amomyrtus spp. Although no more than 10% of fleshy‐fruited propagules reached the margins of the patch, approximately 7% of these were carried there by birds. Every year, canopy gaps (pooling data from edges and centres) concentrated approximately 60% of the total seed rain of both propagule types in both forest patches. Forest margins received less than 20% of the total seed rain, which was largely dominated by fleshy‐fruited species. Seed shadows were a species‐specific attribute rather than a trait associated with propagule type and dispersal mode.

Seed limitation during early forest succession in a rural landscape onChiloé Island,Chile: implications for temperate forest restoration

“…By contrast, seed density of fleshy‐fruited trees was very low – 0·25 ± 0·07 to 2·13 ± 0·48 seeds m −2 day −1 – , and an order of magnitude lower than that observed in nearby upland or riparian forests (Armesto et al . ; Jaña ). Forest interior environments in the same study area, under closed canopy and in canopy gaps, accumulate 17·5 ± 9·75 and 7·5 ± 5·05 seeds m −2 day −1 , respectively (Armesto et al .…”

“…Forest interior environments in the same study area, under closed canopy and in canopy gaps, accumulate 17·5 ± 9·75 and 7·5 ± 5·05 seeds m −2 day −1 , respectively (Armesto et al . ; Jaña ). Such differences suggest that either bird numbers are low in these rural landscapes or there is limited movement of avian‐dispersed seeds from remnant forests into adjacent shrublands.…”

“…These changes are especially relevant in ecosystems where avian seed dispersal has historically played a major role in tree establishment, such as the temperate rain forests of southern South America (Armesto et al . , ; Armesto & Rozzi ).…”

Endozoochory decreases environmental filtering imposed to seedlings

“…), trees on forest edges (Armesto et al. ), or snapped trunks or branches in tree‐fall gaps (Armesto et al. ).…”

Tropical countryside riparian corridors provide critical habitat and connectivity for seed-dispersing forest birds in a fragmented landscape

“…Loss of avian seed dispersers can result in the complete cessation of seed dispersal (Caves et al 2013). Even though the consequences of the loss of large avian seed dispersers have attracted more attention due to their higher vulnerability to extinction (Sekercioglu 2006), seed dispersal by small birds is also important, particularly in tropical forest understory where frugivorous birds are less common than in the higher forest canopy layers (Armesto et al 2001), and small-seeded forest understory shrubs may be dispersal limited (Loiselle and Blake 1999). In contrast to the tropical forest canopy that is species-rich in avian frugivores and seed dispersers, in the frugivore-poor understory, interactions of avian seed dispersers with fruiting plants are thought to be more specific (Loiselle and Blake 1999), and the loss of a single seed disperser species may impact the abundance and distribution of the dispersed plant species significantly more (Howe 1984;Loiselle and Blake 1999).…”